The invention relates to a device and a method for contactless transmission of power or data, in particular an anti-theft protection device for a motor vehicle, in which power or data are exchanged between a stationary unit in the motor vehicle and a portable transponder.
Such devices generally include a stationary unit and a portable unit (transponder) which is disposed, for example, on a smart card or a key. The stationary unit in that case communicates power or energy to the transponder, as a result of which data is sent back by the transponder. An inductively (transformer) coupled coil pair, where each coil is assigned to a respective resonant circuit in the stationary unit and in the transponder, is predominantly provided for that purpose. The data and power transmission is effected therein by a radio-frequency magnetic field by which an oscillation is excited in the other respective resonant circuit.
In that case, both the stationary unit and the transponder can transmit and receive data or power.
In the case of such devices for contactless transmission of power or data, the efficiency is known to be highest when the excitation frequency exciting the resonant circuit corresponds approximately to the resonant frequency of the resonant circuit. However, the resonant frequency of a resonant circuit may be shifted due to component tolerances and temperature influences. Tuning of the resonant circuit, that is to say of the resonant frequency, is therefore necessary.
In a device for contactless transmission of power or data which is known from German Patent DE 38 10 702 C2, the tuning of a resonant circuit is carried out by a regulating circuit through the use of which variable-capacitance diodes are switched into the resonant circuit. The capacitance of the variable-capacitance diodes is changed depending on the regulating voltage, as a result of which the total capacitance of the resonant circuit and thus the resonant frequency are changed. Continuous alteration of the resonant frequency is possible with such a device.
However, such a device enables only capacitive changes of the resonant circuit properties. Since, moreover, the depletion layer in variable-capacitance diodes assumes the function of a capacitor, only slight changing of the capacitances is possible with such a device. In addition, variable-capacitance diodes have large component tolerances. Their blocking behavior and, consequently, their capacitance are changed by the influence of temperature, as a result of which the field of application of such variable-capacitance diodes is very limited.
In a further device which is known from German Patent DE 44 38 287 C1, corresponding to U.S. patent application Ser. No. 08/847,866, filed Apr. 28, 1997, a plurality of capacitors are connected in parallel with the resonant circuit in order to match the resonant frequency to the excitation frequency. However, such a device does not enable continuous, but rather only stepwise matching of the resonant circuit.
It is accordingly an object of the invention to provide a device and a method for contactless transmission of data or power, which overcome the hereinafore-mentioned disadvantages of the heretofore-known devices and methods of this general type and in which a resonant frequency of a transmitting/receiving resonant circuit can be changed continuously and in a wide range.
With the foregoing and other objects in view there is provided, in accordance with the invention, a device for contactless transmission of power (energy) or data, comprising an impedance; a resonant or oscillating circuit generating an alternating magnetic field as a result of oscillation for transmitting power or data, or excited to oscillation by an external alternating magnetic field for receiving power or data, the resonant circuit excited to oscillation at an excitation frequency, and the resonant circuit having components determining a resonant frequency continuously altered by switching in the impedance and matched to the excitation frequency; and a timing control unit for switching the impedance into the resonant circuit only in a phasewise manner in dependence on a difference between the resonant frequency and the excitation frequency in each case within a period of the oscillation.
In accordance with another feature of the invention, the resonant circuit has a capacitor, and the impedance is a capacitor connected in parallel or in series with the capacitor of the resonant circuit.
In accordance with a further feature of the invention, the resonant circuit has a coil, and the impedance is an inductance connected in parallel or in series with the coil.
With the objects of the invention in view, there is also provided a method for contactless transmission of power or data, which comprises providing a resonant circuit generating an alternating magnetic field as a result of oscillation for transmitting power or data, or excited to oscillation by an external alternating magnetic field; determining a resonant frequency of the resonant circuit with components of the resonant circuit; continuously altering the resonant frequency by switching in an impedance and matching the resonant frequency to an excitation frequency; and switching the impedance into the resonant circuit only in a phasewise manner, with a timing control unit, in dependence on a difference between the resonant frequency and the excitation frequency in each case within a period of the oscillation, so that only part of the impedance becomes effective.
The present invention enables the resonant frequency of a resonant circuit to be altered continuously in a simple manner. In this case, the resonant circuit can be altered both capacitively and inductively through the use of an impedance which can be connected only in a phasewise manner. The impedances that are used may be capacitances or inductances having fundamental values which only vary slightly due to temperature influences, as compared with semiconductor components. In addition, such impedances only have small component tolerances.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a device and a method for contactless transmission of power or data, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.